The invention relates to an arrangement for machine reading of information strips with optically encoded information.
Such reading arrangements are used for the machine checking of documents such as identity cards, credit and payment cards, passes, banknotes, stocks and shares and securities, valuable articles or products and the packaging thereof and so forth, which have an information strip with optically encoded information.
EP 0 718 795 A1 discloses a reading arrangement for information strips with optically encoded information. Optical markings are arranged on the information strip in bit lines, wherein at least two bit lines with an identical division into surface portions of equal size are required. Each surface portion is occupied for example by an optical diffraction element. The diffraction elements of the same bit line involve the same grating parameters (spatial frequency, profile shape, azimuth etc) and differ from the diffraction elements of the adjacent bit line. A respective surface portion from the one bit line forms, with the adjacent surface portion from another bit line, a bit pair representing an individual bit of the item of information. In the case of those information strips, after manufacture it is possible for an item of information to be individually written once, wherein in the operation of writing the information in one of the two surface portions of the bit pair, the optical characteristics of the surface portion are irreversibly modified. A number of embodiments of the information strips are described. Specific structures of the diffraction elements are known for example from WO 97/19821 and WO 98/10324.
It is also known (EP 0 883085 A1) for each surface portion of a single-line information strip to be made up from a plurality of partial surfaces which are occupied alternately by one of two different optical diffraction elements from the set a, b, c, d etc. The diffraction elements of one of the sets a, b, c, d etc involve the same grating parameters (spatial frequency, profile shape, azimuth etc) and differ from the diffraction elements of the other sets. Each surface portion differs from its two neighbours by virtue of the choice of the diffraction elements for the partial surfaces. The information of those information strips is the same in all and cannot be individually modified for each information strip.
A bar code which is made up from diffraction elements and a reader which is suitable for labels with such a bar code is described in EP 0 366 858 A1. The information content of that bar code cannot be individually modified.
The reading arrangements described in the quoted documents scan the information by means of a narrow light beam which is incident in perpendicular relationship on to the plane of the information carrier and observe the light which is diffracted at the diffraction elements of the information carrier, by means of photoelectric elements. Those reading arrangements suffer from the disadvantage that the light beam must be moved relative to the information carrier for scanning the information on the information strip.
Without an additional and expensive scanning track on the information carrier, in accordance with EP 0 718 795 A1 the speed of that relative movement must be uniform so that the information which is read off can be recognised.
The reader described in WO 98/55963, instead of the usual discrete photoelectric elements, also uses photodetector arrays which are also known by the name xe2x80x98Charge Coupled Devicexe2x80x99 or CCD. An optical element converts the light emitted from a point source into a parallel light beam which is incident in perpendicular relationship on to the entire face with the optical-diffraction markings, the light beam illuminating at least the entire face with the optical-diffraction markings. The light diffracted at those markings is collected again by the optical element and focused in point form on the photodetector arrays. The reader manages without a relative movement between the incident light and the information strip, and it is substantially independent of the distance between the markings and the optical element. An embodiment can also tolerate azimuth errors. A limitation in terms of the scope of the information has to be accepted as a disadvantage.
The object of the present invention is that of providing a simple and inexpensive arrangement for the machine reading of information strips with optically encoded information, which detects the information with a high level of reliability.
In accordance with the invention the stated object is attained by the features recited in the characterising portion of claim 1. A reading arrangement includes at least one linear detector arrangement which is disposed parallel to a reading plane and behind an optical imaging element and which is directed on to a reading region of the reading plane, lighting devices and an evaluation unit, and serves for the machine reading of an information strip with optically encoded information, which is in the reading region. The light which is diffracted or scattered out of the reading region in which the information strip to be read off by machine is disposed into the optical imaging element is projected on to the photosensitive faces of the detector arrangement in such a way that an image of the reading region is formed. The reading region is laterally inclinedly lit by a respective one of the lighting devices. In a first reading phase the detector arrangement produces detector signals S(1) and in a second reading phase the detector signals S(2), wherein lighting directions xcex1, xcex2, and/or the quality of the light used for lighting the reading region are different in the reading phases. From a comparison of the detector signals S(1) and S(2), the information which is read off is determined and its authenticity verified.
Advantageous configurations of the invention are set forth in the appendant claims.